Method and device for performing channel access in wireless lan

ABSTRACT

A method and device for performing channel access in a wireless LAN are disclosed. An initial channel access method of a station STA in a wireless LAN may include: receiving, from an access point (AP) by the station STA, a frame including information on a channel state, information on a channel access protection section and information on a station STA capable of performing channel access in the channel access protection section; determining a channel access priority by a station STA when the information on the channel state indicates that a wireless link is in a congestion state; and performing initial channel access in the channel access protection section based on the channel access priority determined by the station STA and the information on the station STA capable of performing channel access in the channel access protection section.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and a device for performingchannel access, and more particularly, to a method and a device forperforming channel access of a station (STA).

2. Related Art

In recent years, an evolution direction of a wireless LAN technique hasbeen largely progressed into three directions. As an effort for furtherincreasing a transmission speed on an extension line of the wireless LANevolution direction in the related art, IEEE (institute of electricaland electronic engineers) 802.11ac and IEEE 802.11ad are provided. TheIEEE 802.11ad is a wireless LAN technique using a 60 GHz band. Further,a wideband wireless LAN using a frequency band less than 1 GHz to enablewideband transmission distantively rather than the wireless LAN in therelated art has been come to the fore in recent years and includes IEEE80.211af using a TV white space (TVWS_(—) band and IEEE 802.11ah using a900 MHz band. The wideband LANs mainly aim at extension of a extendedrange Wi-Fi service in addition to a smart grid, and an wideband sensornetwork. Further, a wireless LAN medium access control (MAC) techniquein the related art has a problem that an initial link setup time issignificantly lengthened in some cases. An IEEE 802.11ai standardizationactivity has been recently in progress in order for an STA to rapidlyaccess an AP by solving the problem.

A standardization activity of IEEE 802.11 ai as an MAC technique thathandles a rapid authentication procedure in order to epochally save aninitial set-up and association time of the wireless LAN has been startedas a legal task group in January 2011. In order to enable a rapid accessprocedure, the IEEE 802.11ai has discussed procedure simplification inregions such as AP discovery, network discovery, time synchronizationfunction (TSF) synchronization, authentication and association,procedure merge with a higher layer, and the like. Among them, ideasincluding procedure merge using piggyback of a dynamic hostconfiguration protocol (DHCP), optimization of a full extensibleauthentication protocol (EAP) using a concurrent IP, efficient selectiveaccess point (AP) scanning, and the like have been actively discussed.

SUMMARY OF THE INVENTION

The present invention provides a channel access method.

The present invention also provides an apparatus for performing achannel access method.

In order to achieve the object of the present invention, in an aspect,provided is a method in which a station (STA) performs initial channelaccess in a wireless LAN. The method includes: receiving, by the STA, aframe including information on a channel status, information on aprotected channel access interval, and information on an STA which isaccessible to a channel in the protected channel access interval, froman access point (AP); deciding, by the STA, a channel access prioritywhen the information on the channel status indicates that a radio linkis congested; and performing, by the STA, the initial channel access inthe protected channel access interval based on the decided channelaccess priority and the information on the STA which is accessible tothe channel in the protected channel access interval, wherein theinformation on the protected channel access interval includesinformation on a time limited so as for only the STA which is accessibleto the channel in the protected channel access interval to performschannel access.

In order to achieve the object of the present invention, in anotheraspect, provided is a station for performing scanning in a wireless LAN.The station includes: an RF unit receiving a radio signal; and aprocessor selectively connected with the RF unit, wherein the processoris implemented to receive a frame including information on a channelstatus, information on a protected channel access interval, andinformation on an STA which is accessible to a channel in the protectedchannel access interval, from an access point (AP), decide a channelaccess priority when the information on the channel status indicatesthat a radio link is congested, and perform initial channel access inthe protected channel access interval based on the decided channelaccess priority and the information on the STA which is accessible tothe channel in the protected channel access interval, and theinformation on the protected channel access interval includesinformation on a time limited so as for only the STA which is accessibleto the channel in the protected channel access interval to performschannel access.

Initial link setup can be rapidly performed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram illustrating a structure of a wirelesslocal area network (WLAN).

FIG. 2 is a diagram illustrating a hierarchical architecture of awireless LAN system supported by IEEE 802.11.

FIG. 3 is a conceptual diagram illustrating a scanning method in thewireless LAN.

FIG. 4 is a conceptual diagram illustrating an authentication andassociation process after scanning of an AP and an STA.

FIG. 5 is a conceptual diagram of an active scanning procedure.

FIG. 6 is a conceptual diagram illustrating a method for transmitting aprobe request frame.

FIG. 7 is a conceptual diagram illustrating a channel access method ofthe STA based on a distributed coordination function (DCF).

FIG. 8 is a conceptual diagram illustrating a back-off procedure of aplurality of STAs.

FIG. 9 is a conceptual diagram illustrating an inter-frame space.

FIG. 10 is a conceptual diagram illustrating a method for acquiring atransmit opportunity (TXOP) of the STA.

FIG. 11 is a conceptual diagram illustrating an enhanced distributedchannel access (EDCA) channel reference model.

FIG. 12 is a conceptual diagram illustrating a back-off procedure of theEDCA.

FIG. 13 is a conceptual diagram illustrating a polled TXOP timing.

FIG. 14 is a conceptual diagram illustrating an initial link configuringmethod according to an embodiment of the present invention.

FIG. 15 is a conceptual diagram illustrating a frame includinginformation on a channel access protection section according to anembodiment of the present invention.

FIG. 16 is a conceptual diagram illustrating an initial access method ofan STA according to an embodiment of the present invention.

FIG. 17 is a conceptual diagram illustrating a channel access method ofan STA depending on a scanning access class according to an embodimentof the present invention.

FIG. 18 is a conceptual diagram illustrating a frame format according toan embodiment of the present invention.

FIG. 19 is a conceptual diagram illustrating a frame format according tothe embodiment of the present invention.

FIG. 20 is a conceptual diagram illustrating a channel access method ofan STA according to an embodiment of the present invention.

FIG. 21 is a conceptual diagram illustrating a channel access method ofan STA according to an embodiment of the present invention.

FIG. 22 is a conceptual diagram illustrating a frame format according tothe embodiment of the present invention.

FIG. 23 is a block diagram illustrating a wireless apparatus to whichthe embodiment of the present invention can be applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a concept view illustrating the structure of a wireless localarea network (WLAN).

FIG. 1(A) shows the structure of the IEEE (institute of electrical andelectronic engineers) 802.11 infrastructure network.

Referring to FIG. 1(A), the WLAN system may include one or more basicservice sets (BSSs, 100 and 105). The BSS 100 or 105 is a set of an APsuch as AP (access point) 125 and an STA such as STA1 (station) 100-1that may successfully sync with each other to communicate with eachother and is not the concept to indicate a particular area. The BSS 105may include one AP 130 and one or more STAs 105-1 and 105-2 connectableto the AP 130.

The infrastructure BSS may include at least one STA, APs 125 and 130providing a distribution service, and a distribution system (DS) 110connecting multiple APs.

The distribution system 110 may implement an extended service set (ESS)140 by connecting a number of BSSs 100 and 105. The ESS 140 may be usedas a term to denote one network configured of one or more APs 125 and230 connected via the distribution system 110. The APs included in oneESS 140 may have the same SSID (service set identification).

The portal 120 may function as a bridge that performs connection of theWLAN network (IEEE 802.11) with other network (for example, 802.X).

In the infrastructure network as shown in FIG. 1(A), a network betweenthe APs 125 and 130 and a network between the APs 125 and 130 and theSTAs 100-1, 105-1, and 105-2 may be implemented. However, without theAPs 125 and 130, a network may be established between the STAs toperform communication. The network that is established between the STAswithout the APs 125 and 130 to perform communication is defined as anad-hoc network or an independent BSS (basic service set).

FIG. 1(B) is a concept view illustrating an independent BSS.

Referring to FIG. 1(B), the independent BSS (IBSS) is a BSS operating inad-hoc mode. The IBSS does not include an AP, so that it lacks acentralized management entity. In other words, in the IBSS, the STAs150-1, 150-2, 150-3, 155-4, and 155-5 are managed in a distributedmanner. In the IBSS, all of the STAs 150-1, 150-2, 150-3, 155-4, and155-5 may be mobile STAs, and access to the distribution system is notallowed so that the IBSS forms a self-contained network.

The STA is some functional medium that includes a medium access control(MAC) following the IEEE (Institute of Electrical and ElectronicsEngineers) 802.11 standards and that includes a physical layer interfacefor radio media, and the term “STA” may, in its definition, include bothan AP and a non-AP STA (station).

The STA may be referred to by various terms such as mobile terminal,wireless device, wireless transmit/receive unit (WTRU), user equipment(UE), mobile station (MS), mobile subscriber unit, or simply referred toas a user.

FIG. 2 is a view illustrating a layer architecture of a WLAN systemsupported by IEEE 802.11.

FIG. 2 conceptually illustrates a layer architecture (PHY architecture)of a WLAN system.

The WLAN system layer architecture may include an MAC (medium accesscontrol) sub-layer 220, a PLCP (Physical Layer Convergence Procedure)sub-layer 210, and a PMD (Physical Medium Dependent) sub-layer 200. ThePLCP sub-layer 210 is implemented so that the MAC sub-layer 220 isoperated with the minimum dependency upon the PMD sub-layer 200. The PMDsub-layer 200 may serve as a transmission interface to communicate databetween a plurality of STAs.

The MAC sub-layer 220, the PLCP sub-layer 210, and the PMD sub-layer 200may conceptually include management entities.

The management entity of the MAC sub-layer 220 is denoted an MLME (MAClayer management entity, 225), and the management entity of the physicallayer is denoted a PLME (PHY layer management entity, 215). Suchmanagement entities may offer an interface where a layer managementoperation is conducted. The PLME 215 is connected with the MLME 225 tobe able to perform a management operation on the PLCP sub-layer 210 andthe PMD sub-layer 200, and the MLME 225 is also connected with the PLME215 to be able to perform a management operation on the MAC sub-layer220.

There may be an SME (STA management entity, 250) to perform a proper MAClayer operation. The SME 250 may be operated as a layer independentcomponent. The MLME, PLME, and SME may communicate information betweenthe mutual components based on primitive.

The operation of each sub-layer is briefly described below. The PLCPsub-layer 110 delivers an MPDU (MAC protocol data unit) received fromthe MAC sub-layer 220 according to an instruction from the MAC layerbetween the MAC sub-layer 220 and the PMD sub-layer 200 to the PMDsub-layer 200 or delivers a frame from the PMD sub-layer 200 to the MACsub-layer 220. The PMD sub-layer 200 is a PLCP sub-layer and the PMDsub-layer 200 may communicate data between a plurality of STAs by way ofa radio medium. The MPDU (MAC protocol data unit) delivered from the MACsub-layer 220 is denoted a PSDU (Physical Service Data Unit) on the sideof the PLCP sub-layer 210. The MPDU is similar to the PSDU, but in casean A-MPDU (aggregated MPDU), which is obtained by aggregating aplurality of MPDUs, has been delivered, each MPDUs may differ from thePSDU.

The PLCP sub-layer 210 adds an additional field including informationrequired by the physical layer transceiver while receiving the PSDU fromthe MAC sub-layer 220 and delivering the same to the PMD sub-layer 200.In this case, the added field may include a PLCP preamble to the PSDU, aPLCP header, and tail bits necessary to return the convolution encoderto zero state. The PLCP preamble may play a role to allow the receiverto prepare for syncing and antenna diversity before the PSDU istransmitted. The data field may include padding bits to the PSDU, aservice field including a bit sequence to initialize the scrambler, anda coded sequence in which a bit sequence added with tail bits has beenencoded. In this case, as the encoding scheme, one of BCC (BinaryConvolutional Coding) encoding or LDPC (Low Density Parity Check)encoding may be selected depending on the encoding scheme supported bythe STA receiving the PPDU. The PLCP header may include a fieldcontaining information on the PPDU (PLCP Protocol Data Unit) to betransmitted.

The PLCP sub-layer 210 adds the above-described fields to the PSDU togenerate the PPDU (PLCP Protocol Data Unit) and transmits the same to areceiving station via the PMD sub-layer 200, and the receiving stationreceives the PPDU and obtains information necessary for data restorationfrom the PLCP preamble and PLCP header to thus restore the same.

FIG. 3 is a concept view illustrating a scanning method in a WLAN.

Referring to FIG. 3, the scanning method may be divided into passivescanning 300 and active scanning 350.

Referring to FIG. 3(A), the passive scanning 300 may be performed by abeacon frame 330 that is periodically broadcast from the AP 300. The AP300 in the WLAN broadcasts the beacon frame 330 to the non-AP STA 340 ata particular period (e.g., per 100 msec). The beacon frame 330 maycontain information on the current network. The non-AP STA 340 mayperform scanning on the channel with the AP 310 to perform theauthentication/association process by obtaining the network informationfrom the beacon frame 330 periodically broadcast.

The passive scanning method 300 only receives the beacon frame 330transmitted from the AP 310 without the need for the non-AP STA 340 totransmit a frame. Accordingly, the passive scanning 300 is advantageousof a reduction in the overall overhead that is created upon datatransmission/reception over the network. However, since the scanning isobliged to be passively performed in proportion to the period of thebeacon frame 330, the time taken to perform scanning may be increased.The details of the beacon frame are set forth in IEEE DraftP802.11-REVmb™/D12, November 2011 ‘IEEE Standard for InformationTechnology Telecommunications and information exchange betweensystems—Local and metropolitan area networks—Specific requirements Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)Specifications (hereinafter, IEEE 802.11)’ 8.3.3.2 beacon framedisclosed on November, 2011. IEEE 802.11ai may additionally use otherformat of a beacon frame, and such beacon frame may be referred to as aFILS (fast initial link setup) beacon frame. Further, the measurementpilot frame is a frame containing only some information of the beaconframe, and the measurement pilot frame may be used in the scanningprocedure. The measurement pilot frame is set forth in IEEE 802.118.5.8.3 measurement pilot format.

Further, a fast initial link setup (FILS) discovery frame may bedefined. The FILS discovery frame as a frame transmitted during atransmission cycle of the beacon frame at each AP may be a frametransmitted at a shorter cycle than the beacon frame. That is, the FILSdiscovery frame is a frame transmitted at a cycle having a smaller valuethan the transmission cycle. The FILS discovery frame may includeidentifier information (SSID and BSSID) of the AP that transmits thediscovery frame. The FILS discovery frame is transmitted before thebeacon frame is transmitted to the STA to allow the STA to discover thatthe AP exists in the corresponding channel in advance. An interval oftransmitting the FILS discovery frame in one AP is referred to as anFILS discovery frame transmission interval. Some of the informationincluded in the beacon frame is included in the FILS discovery frame,which may be transmitted. Some of the information included in the beaconframe is included in the FILS discovery frame, which may be transmitted.The FILS discovery frame may include even information on a transmissiontime of the beacon frame of a neighboring AP.

Referring to FIG. 3(B), the active scanning 350 refers to a method inwhich the non-AP STA 390 leads scanning by transmitting a probe requestframe 370 to the AP 360.

After receiving the probe request frame 370 from the non-AP STA 390, theAP 360 may wait a random time to prevent frame collision, and the AP 360then includes network information in a frame response frame 380, thensending the same to the non-AP STA 390. The non-AP STA 390 may obtainthe network information based on the received probe response frame 380to stop the scanning process.

The active scanning 350 allows the non-AP STA 390 to lead the scanningprocess, and the active scanning 350 has the advantage of a shortscanning time. However, the non-AP STA 390 should transmit the proberequest frame 37, resulting in an increase in the network overhead forframe transmission and reception. The probe request frame 370 is setforth in IEEE 802.11 Ch. 8.3.3.9, and the probe response frame 380 isset forth in IEEE 802.11 Ch. 8.3.3.10.

After the scanning is done, the AP and the STA may conduct anauthentication and association procedure.

FIG. 4 is a concept view illustrating an authentication and associationprocess after scanning between an AP and an STA.

Referring to FIG. 4, after passive/active scanning, the authenticationand association may be conducted with one of the scanned APs.

The authentication and association process may be carried out by way of,e.g., 2-way handshaking. FIG. 4(A) is a concept view illustrating anauthentication and association process after passive scanning, and FIG.4(B) is a concept view illustrating an authentication and associationafter active scanning.

The authentication and association process may be equally performed byexchanging an authentication request frame 410/authentication responseframe 420 and an association request frame 430/association responseframe 440 between the AP 400 or 450 and the non-AP STA 405 or 455regardless of which one of the active scanning method and the passivescanning method has been used.

The authentication process may be conducted by transmitting theauthentication request frame 410 from the non-AP STA 405 or 455 to theAP 400 or 450. In response to the authentication request frame 410, theauthentication response frame 420 may be transmitted from the AP 400 or450 to the non-AP STA 405 or 455. The authentication frame format is setforth in IEEE 802.11 Ch. 8.3.3.11.

The association process may be conducted by transmitting the associationrequest frame 430 from the non-AP STA 405 or 455 to the AP 400 or 405.In response to the association request frame 430, the associationresponse frame 440 may be transmitted from the AP 405 or 455 to thenon-AP STA 400 or 450. The transmitted association request frame 430contains information on the capability of the non-AP STA 405 or 455.Based on the information on the capability of the non-AP STA 405 or 455,the AP 400 or 350 may determine whether the non-AP STA 405 or 355 may besupported. In case such support is possible, the AP 300 or 450 mayinclude in the association response frame 440 whether to accept theassociation request frame 440 and a reason therefore, and itssupportable capability information, and the AP 300 or 450 may send thesame to the non-AP STA 405 or 455. The association frame format is setforth in IEEE 802.11 Chs. 8.3.3.5/8.3.3.6.

After the association step is done, normal data transmission andreception is carried out. The association, unless done, is re-conductedbased on the reason for which the association is not performed, orassociation with other AP may be performed.

FIG. 5 is a concept view illustrating an active scanning procedure.

Referring to FIG. 5, the active scanning procedure may be performed inthe following steps.

(1) It is determined whether the STA 500 is ready to perform thescanning procedure.

The STA 500 may wait, e.g., until the probe delay time expires orparticular signaling information (for example, PHY-RXSTART.indicationprimitive) is received to perform active scanning.

The probe delay time is a delay that occurs before the STA 500 sends aprobe request frame 510 when performing active scanning.PHY-RXSTART.indication primitive is a signal that is transmitted fromthe physical (PHY) layer to the local MAC (medium access control) layer.PHY-RXSTART.indication primitive may signal information indicating thatthe PLCP (physical layer convergence protocol) has received a PPDU (PLCPprotocol data unit) including a valid PLCP header to the MAC layer.

(2) Basic access is performed.

In the 802.11 MAC layer, a number of STAs may share a radio medium usinga distributed coordination function (DCF) that is a contention-basedfunction. The DCF may prevent collision between STAs through a back-offscheme using the carrier sense multiple access/collision avoidance(CSMA/CA) as its access protocol. The STA 500 may transmit the proberequest frame 510 to the APs 560 and 570 using a basic access method.

(3) Information for specifying the APs 560 and 570 included inMLME-SCAN.request primitive (for example, SSID (service setidentification) and BSSID (basic service set identification)information) may be included in the probe request frame 510 and may betransmitted.

The BSSID may have a value corresponding to the MAC address of the AP asan indicator to specify the AP. The SSID (service set identification) isa network term for specifying an AP, which may be read by a person whooperates the STA. The BSSID and/or SSID may be used to specify an AP.

The STA 500 may specify an AP based on the information to specify theAPs 560 and 570 included by MLME-SCAN.request primitive. The specifiedAPs 560 and 570 may send the probe response frames 550 and 550 to theSTA 500. The STA 500 may include the SSID and BSSID information in theprobe request frame 510 and send the same, thereby unicasting,multicasting, or broadcasting the probe request frame 510. A method ofunicasting, multicasting, or broadcasting the probe request frame 510using the SSID and BSSID information is further described with referenceto FIG. 5.

For example, in case an SSID list is included in MLME-SCAN.requestprimitive, the STA 500 may include the SSID list in the probe requestframe 510 and transmit the same. The APs 560 and 570 may receive theprobe request frame 510, determine the SSIDs included in the SSID listcontained in the received probe request frame 510, and determine whetherto send the probe response frames 550 and 550 to the STA 200.

(4) A probe timer is initialized as 0 and is then operated.

The probe timer may be used to check a minimum channel time(MinChanneltime, 520) and a maximum channel time (MaxChanneltime, 530).The minimum channel time 520 and the maximum channel time 530 may beused to control the active scanning operation of the STA 500.

The minimum channel time 520 may be used to perform the operation forvarying the channel for conducting active scanning. For example, in casethe STA 500 fails to receive the probe response frames 550 and 550 untilthe probe timer get to the minimum channel time 520, the STA 500 shiftsscanning channels to perform scanning on other channel. In case the STA500 receives the probe response frame 550 until the probe timer get tothe minimum channel time 520, it may process the received probe responseframes 540 and 550 after waiting until the probe timer get to themaximum channel time 530.

The STA 500 may detect PHY-CCA.indication primitive until the probetimer reaches the minimum channel time 520 and may determine whetherother frame (for example, probe response frames 550 and 550) has beenreceived by the STA 500 until before the minimum channel time 520.

PHY-CCA.indication primitive may transmit information on the state ofthe medium from the physical layer to the MAC layer. PHY-CCA.indicationprimitive may indicate the current state of the channel using channelstate parameters such as “busy” when the channel is unavailable and“idle” when the channel is available. The STA 500 may determine thatthere are probe response frames 550 and 550 received by the STA 500 whenPHY-CCA.indication is detected to be busy and may determine that thereare no probe response frames 550 and 550 received by the STA 500 whenPHY-CCA.indication is detected to be idle.

In case PHY-CCA.indication is detected to be idle, the STA 500 may setan NAV (net allocation vector) to 0, and the STA 500 may scan a nextchannel. In case PHY-CCA.indication is detected to be busy, the STA 500may perform a process on the received probe response frames 550 and 550after the probe timer reaches the maximum channel time 530. After theprocess on the received probe response frames 550 and 550 is done, theSTA 500 may set the NAV (net allocation vector) to 0 and may then scan anext channel.

Hereinafter, in embodiments of the present invention, determiningwhether there are probe response frames 550 and 550 received by the STA500 may also mean that the channel state is determined usingPHY-CCA.indication primitive.

(5) In case all the channels included in the channel list (ChannelList)are scanned, the MLME may signal MLME-SCAN.confirm primitive.MLME-SCAN.confirm primitive may contain BSSDescriptionSet including allthe information obtained in the scanning process.

In case the STA 500 uses the active scanning method, the STA 500 shouldperform monitoring to determine whether the parameter ofPHY-CCA.indication is busy until the probe timer reaches the minimumchannel time.

The specific information included in the above-described MLME-SCAN is asfollows. In order for the STA to perform scanning, the MLME may receiveMLME-SCAN.request primitive. MLME-SCAN.request primitive is a primitivecreated by the SME. MLME-SCAN.request primitive may be used to determinewhether there is other BSS to which the STA is to be connected.

MLME-SCAN.request primitive may contain information specifically such asBSSType, BSSID, SSID, ScanType, ProbeDelay, ChannelList, MinChannelTime,MaxChannelTime, Requestlnformation, SSID List, ChannelUsage,AccessNetworkType, HESSID, MeshID, VendorSpecificInfo. The details ofMLME-SCAN.request primitive are set forth in IEEE DraftP802.11-REVmb™/D12, November 2011 ‘IEEE Standard for InformationTechnology Telecommunications and information exchange betweensystems—Local and metropolitan area networks—Specific requirements Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)Specifications’ 6.3.3.2 MLME-SCAN.request disclosed on November, 2011.

The following Table 1 briefly represents example information included inMLME-SCAN.request primitive.

TABLE 1 name description BSSType Determines whether infrastructure BSS,IBSS, MBSS (Mesh basic service set), or all, are included in the scanBSSID Identifies a specific or wildcard BSSID SSID Specifies the desiredSSID or the wildcard SSID ScanType Indicates either active or passivescanning ProbeDelay Delay(in microseconds) to be used prior totransmitting a probe frame during active scanning ChannelList Specifiesa list of channels that are examined when scanning for a BSSMinChannelTime The minimum time(in TU) to spend on each channel whenscanning MaxChannelTime The maximum tine(in TU) to spend on each channelwhen scanning Require- This element is optionally present ifmentInformation dot11RadioMeasurementActivated is true and is placed ina Probe Request frame to request that the responding STA include therequested information in the Probe Response frame SSID List One or moreSSID elements that are optionally present whendot11MgmtOptionSSIDListActivated is true ChannelUsage Specific requesttypes for the ChannelUsage request AccessNet- Specifies a desiredspecific access network type or the workType wildcard access networktype HESSID Specifies the desired specific HESSID network identifier orthe wildcard network identifier. This field is present whendot11InterworkingSeviceAc- tivated is true Mesh ID Only present ifBSSType = MESH or BSSType = ANY_BSS. Specifies the desired Mesh ID orwildcard Mesh ID. RequestParam- The parameters define the respondingSTAs eters ReportingOption Indicates the result reporting modeAPConfigura- When a specific BSSID is indicated in the tionChangeCountMLME-SCAN.request, the APConfigurationChangeCount associated with thestored configuration of the AP is optionally provided VendorSpe-Information added according to each of vendors cificInfo

The request parameter included in MLME-SCAN.request primitive may beused to determine whether the responding STA is to transmit a proberesponse frame. The request parameter may contain information forrequesting that other BSS's information be included in the proberesponse frame. Also, the request parameter may include a report requestfield, a delay reference field, and a maximum delay limit field.

The report request field contains information to request that otherBSS's information be included in the probe response frame, the delayreference field contains information on the delay type applied as aresponse to the probe request frame, and the maximum delay limit fieldmay contain the maximum access delay information on the delay typeindicated by the delay reference field.

Besides, the request parameter may include a minimum data rate fieldand/or a received signal strength limit field. The minimum data ratefield contains information on the lowest overall data rate intransmitting an MSDU or A-MSDU. The received signal strength limit fieldmay further contain information on the limit value of the signalnecessary for a recipient of the probe request frame to respond.

FIG. 6 is a conceptual diagram illustrating a method for transmitting aprobe request frame.

In FIG. 6, a method in which the STA broadcasts, multicasts, andunicasts the probe request frame is disclosed.

FIG. 6(A) illustrates a method in which the STA 600 broadcasts the proberequest frame 610.

The STA 600 encapsulates a widecard SSID and a widecard BSSID in theprobe request frame 610 to broadcast the probe request frame 610.

The wildcard SSID and the wildcard BSSID may be used as identifiers forindicating all of APs 606-1, 606-2, 606-3, 606-4, and 606-6 included ina transmission range of the STA 600.

The STA 600 transmits the probe request frame 610 including the wildcardSSID and the wildcard BSSID, the APs 606-1, 606-2, 606-3, 606-4, and606-6 that receive the probe request frame 610 transmitted by the STA600 may transmit a probe response frame to the STA 600 as a response tothe received probe request frame.

When the response frame is transmitted to the STA 600 as the response tothe probe request frame 610 received by the APs 606-1, 606-2, 606-3,606-4, and 606-6 that receives the broadcasted probe request frame 610for a predetermined time, a problem that the STA 600 should receive andprocess too many probe response frames at once may occur.

FIG. 6(B) illustrates a method in which the STA 620 UNIbroadcasts theprobe request frame 630.

Referring to FIG. 6(B), when the STA 620 unicasts the probe requestframe 630, the STA 620 may transmit the probe request frame 630including specific SSID/BSSID information of the AP. Only an AP 626corresponding to an SSID/BSSID specified by the STA 620 among APs thatreceive the probe request frame 630 may transmit the probe responseframe to the STA 620.

FIG. 6(C) illustrates a method in which the STA 640 multicasts the proberequest frame 660.

Referring to FIG. 6(C), the STA 640 may transmit the probe request frame660 including an SSID list and the wildcard BSSID. APs 660-1 and 660-2corresponding to an SSID included in the SSID list included in the proberequest frame among AP that receive the probe request frame 660 IDspecified by the STA 660 among APs that receive the probe request frame630 may transmit the probe response frame to the STA 640.

In performing the scanning procedure, the STA senses a channel during aprobe delay interval whether the frame received through the channelexists.

The active scanning procedure in the related art will be describedbelow. The STA may receive MLME-SCAN-request primitive to instructactive scanning generated in an MLME. The STA may determine a (unicast,multicast, or broadcast) method for transmitting the probe request framebased on the MLME-SCAN-request primitive and further, determine theBSSID and the SSID to be included in the probe request frame.

The STA may determine whether the probe delay time is terminated and avalid frame is received by a PHY layer of the STA. The probe delay maybe used as a channel discovery interval which the STA performing theactive scanning uses before transmitting the probe request frame. Forexample, when the valid frame is received by the PHY layer, the PHYlayer of the STA generates specific primitive (for example,PHYRxStart.indication primitive) to transmit the generated primitive toan MAC layer. When the probe delay time is terminated and the validframe is received by the PHY layer of the STA, the STA may performchannel access in order to transmit the probe request frame to thechannel. When the STA succeeds in the channel access, the STA maytransmit the probe request frame to the channel.

The STA may transmit the probe request frame and set a probe timer. TheSTA may measure a channel status until the probe timer reaches a minimumchannel time. When the channel status is not busy according to ameasurement result of the channel status of the STA, the STA may set NAVto 0 and scan another channel. When the channel status is busy accordingto the measurement result of the channel status of the STA, the STA mayreceive the probe response frame from the channel until the probe timerreaches a maximum channel time. The STA may process all of proberesponse frames which are received when the probe timer reaches themaximum channel time. Whether the channel status sensed by the STA isbusy may be determined based on PHY-CCA.indication primitive generatedby the PHY layer of the STA.

Herein, a wireless access method used in 802.11 will be disclosed.

A plurality of STAs may share a radio medium based on the distributedcoordination function (DCF) performed by the MAC layer. The DCF is basedon carrier sensing multiple access with collision avoidance (CSMA/CA).The plurality of STAs may share the medium based on request to send(RTS)/clear to send (CTS) selectively performed by the MAC layer. TheDCF may be configured so as for the plurality of STAs to share the radiomedium based on the following operation in detail.

FIG. 7 is a concept view illustrating a channel access of a STA based ona DCF access process.

Generally, In the method for the channel access of the STA based on aDCF, the STA may transmit an immediate MPDU (MAC Protocol Data Unit) ifa medium is not used for a DCF interframe space (DIFS) period or more(i.e., if the channel is idle during DIFS). In case the medium isdetermined to be in use by a carrier sensing mechanism by the STA, theSTA may determine the size of a CW (Contention Window) by a randombackoff algorithm and may perform a backoff procedure. In order toperform the backoff procedure, the STA sets up the CW and selects sometime slot. The selected time slot is called a backoff time. Among aplurality of STAs, a STA having the relatively short backoff time mayaccess the medium faster than a STA having the relatively long backofftime. The other STAs may stop the remaining backoff time and wait untiltransmitting a frame of an accessed STA is completed. After thetransmission of frame of the accessed STA is complete, the other STAsconduct contention over the remaining backoff time to obtain the medium.

In other words, in case the STA gains access to a channel using the DCF,the STA may detect the channel state for a predetermined time.Specifically, the STA, in case the channel remains idle during DIFS,attempts transmission after a random backoff time. Such DCF-basedtransmission scheme plays a role to avoid a plurality of STAs from asimultaneous transmission of frames, thus preventing collision.

The random backoff time is a time period during which the STA waitsbefore a frame is transmitted after waiting a predetermined time (forexample, DIFS), and the random backoff time may be defined as in thefollowing equation 1:

Backoff time=Random( )×SlotTime  <Equation 1>

-   -   Random( )=an integer between 0 and CW    -   CW is an integer between CWmin and CWmax

In short, the STA may determine a CW based on the CWmin which is theminimum CW time, and the CWmax which is the maximum CW time. The STA maydetermine the backofftime based on the determined CW.

FIG. 8 is a concept view illustrating a backoff procedure of a pluralityof STAs.

Referring to FIG. 8, a backoff slot may occur after a medium isdetermined to be idle for a DIFS period. If no activity of the medium isdetected after DIFS, the STA may reduce the backoff time based onaSlotTime. In case the medium is determined to be in use for the backoffslot, the STA might not reduce the backoff time. The frame transmissionof the STA may be performed whenever a set backoff timer is 0.

Further, in the DCF transmission scheme an RTS/CTS access mode may beused. When the RTS/CTS access mode is used, control frames (RTS, CTS)are exchanged before a data frame is transmitted to pre-occupy achannel. Such scheme may reduce channel waste by replacing a collisionthat may occur upon transmission of a data frame with a collision by arelatively short control frame.

As another method for sharing a radio medium by a plurality of STAs, theMAC layer can use a PCF (Point Coordination Function). Theabove-described DCF is based on the CSMA/CA scheme and is thus not ableto guarantee real-time transmission of data transmitted between an STAand an AP. In contrast, the PCF which is a transmission method based ona non-contention may be used as a method to guarantee QoS (Quality OfService) upon real-time data transmission. The PCF, also known as anon-contentious transmission service, may be used alternately with aDCF-type contention-based service, rather than exclusively using theentire medium transmission period. In the PCF, a point coordinatorimplemented in the AP of the BSS may control the right for each STA tobe able to occupy the medium using a polling scheme. The PCF may begiven a priority over the DCF by setting the PIFS, which is an IFS(Inter-Frame Space) in the PCF, to be smaller than the DIFS, which is anIFS of the DCF. The IFS denotes an interval between frames, and the IFSmay be used to set a priority in which an STA accesses the medium. TheIFS may be specifically defined as follows.

FIG. 9 is a concept view illustrating a interframe space (IFS).

Referring to FIG. 9, the interval between two frames may be referred toas an IFS. An STA may determine whether a channel is being used for atime period of the IFS as previously defined, using a carrier sensingscheme. The MAC layer using the DCF defines various IFSs. The priorityof an STA occupying a radio medium may be determined by an IFS.Inter-frame intervals depending on types of IFSs are as follow:

(1) SIFS (Short Inter Frame Symbol): used upon RTS/CTS, ACK frametransmission. Highest priority

(2) PIFS (PCF IFS): used upon PCF frame transmission

(3) DIFS (DCF FIS): used upon DCF frame transmission

(4) EIFS (Extended IFS): used only when frame transmission error occurs.Not fixed interval

In case the DCF is used only for a plurality of STAs to share a radiomedium at the MAC layer, various problems may arise. For example, whenthe DCF is used, if a plurality of STAs simultaneously conduct initialaccess to an AP, collision frequently occurs between the plurality ofSTAs. Further, the DCF lacks the concept of transmission priority and isnot thus able to guarantee QoS (Quality Of Service) for traffic datatransmitted from an STA. To address such issues, 802.11e defines a newcoordination function, HCF (Hybrid Coordination Function), to enhancethe channel access capability of the existing DCF and HCF. The HCFdefines two channel access schemes, HCCA (HCF Controlled Channel Access)and EDCA (Enhanced Distributed Channel Access), similar to those definedin 802.11 MAC.

The EDCA and HCCA defines traffic categories that are transmissionpriorities, and the EDCA and HCCA may determine priorities at whichchannel access is conducted. In other words, the EDCA and HCCA maydetermine channel access priorities depending on types of traffic databy mutually defining a CW and an IFS according to the category oftraffic data transmitted from an STA.

For example, in case traffic data is an email, the data may be allocatedto a low priority class. As another example, in case traffic data is avoice communication through a wireless LAN, channel access may beconducted, with the traffic data allocated to a high priority classbecause the data for the voice communication is data needed for a realtime data transmission.

Upon use of the EDCA, traffic data with a higher priority would haverelatively more chance to be transmitted as compared with traffic datawith a lower priority. Further, an STA having higher-priority trafficmay have a shorter average wait time than an STA having lower-prioritytraffic before transmitting packets. A transmission priority in the EDCAmay be implemented by allocating a shorter CW to higher-priority trafficrather than lower-priority traffic while assigning an AIFS (Arbitrationinter-Frame Space) that is shorter than the IFS that is a frame intervaldefined in the DCF. Further, the EDCA enables an STA to access a channelwithout contention during a period that is referred to as a TXOP(Transmit Opportunity). An STA may transmit as many packets as possibleduring a predetermined TXOP period within a range not exceeding themaximum period of the TXOP. If one frame is too long to be transmittedduring one TXOP, the frame may be cut into smaller frames that may bethen transmitted. Use of the TXOP may mitigate the situation that an STAwith a low transmission rate excessively occupies a channel, which is aproblem of the existing 802.11 DCF MAC.

FIG. 10 is a concept view illustrating a method of obtaining a TXOP byan STA.

Referring to FIG. 10, an STA attending QoS transmission may use twochannel access schemes such as EDCA and HCCA to obtain a TXOP by whichthe STA may transmit traffic for a predetermined traffic. The TXOP maybe obtained by succeeding in an EDCA contention or by receiving a QoSCF-Poll frame from an access point. The TXOP obtained by succeeding inan EDCA contention is called an EDCA TXOP, and a TXOP obtained byreceiving a QoS CF-Poll frame from an AP is called a Polled TXOP. Assuch, use of the concept “TXOP” enables an STA to be given apredetermined time during which the STA may transmit a frame or enablesthe transmission time of the STA to be forcedly constrained. Thetransmission start time and maximum transmission time of a TXOP may bedetermined by an AP. The EDCA TXOP may be notified to an STA by a beaconframe, and the Polled TXOP may be notified to an STA by a QoS CF-Pollframe.

The EDCA and HCCA which are channel access schemes defined in the HCFare hereinafter described in greater detail.

(1) EDCA

In the EDCA scheme, channel access may be conducted with a plurality ofuser priorities (for example, 8 user priorities) defined for trafficdata. For priority-based QoS data frame transmission, the EDCA definesfour ACs (Access Categories: AC_BK, AC_BE, AC_VI, and AC_VO). The EDCAmay, based on the ACs, map the traffic data arriving at the MAC layerwith different user priorities as in the following <Table 2>.

Table 2 exemplifies the mapping between the user priorities and the ACs.

TABLE 2 Priority User Priority AC(access category) Low 1 AC_BK 2 AC_BK 0AC_BE 3 AC_BE 4 AC_VI 5 AC_VI 6 AC_VO High 7 AC_VO

A transmission queue and access category or access class (AC) parametermay be defined for each AC. The differences in transmission prioritybetween the ACs may be implemented based on the AC parameter values setto be different from each other. The AC parameters are access parameterinformation to determine the channel access method according to each ofACs. The EDCA may use AIFS[AC], CWmin[AC], and CWmax[AC] instead ofDIFS, CWmin, and CWmax, respectively, which are parameters used in theDCF in the backoff procedure for transmitting the frames belonging tothe AC. The parameters used in the backoff procedure for each AC may becarried over a beacon frame from an AP to each STA. As AIFS[AC] andCWmin[AC] decrease, a higher priority is given, and accordingly, thechannel access delay shortens, thus allowing for use of more bands in agiven traffic environment.

In case a collision occurs between the STAs while the STA transmits aframe, an EDCA backoff procedure of generating a new backoff counter issimilar to the existing DCF backoff procedure, and differentiatedbackoff procedures for each AC may be performed based on different EDCAparameters. The EDCA parameters is becoming a critical means todifferentiate channel access of various user priorities of traffic. Aproper configuration of the EDCA parameter value including per-ACparameters may increase the transmission effect according to thepriority of traffic while optimizing the network performance.Accordingly, an AP should conduct the overall management and adjustmentfunction for the EDCA parameters to ensure that all of the STA attendingthe network may evenly access the medium.

FIG. 11 is a concept view illustrating an EDCA channel reference model.

Referring to FIG. 11, the transmission queue for each of the four ACsdefined in 802.11e MAC may play a role as an individual EDCA contentionentity for radio medium access in one STA. One AC may retain anindependent backoff counter with its own AIFS value. If there are one ormore ACs that have simultaneously finished backoff, the collisionbetween the ACs may be adjusted by a virtual collision handler. A frameis first transmitted to an AC having the highest priority, and the otherACs renew their backoff counters by increasing the contentious windowvalues.

The start of a TXOP occurs upon accessing a channel according to theEDCA rules. If obtaining an EDCA TXOP when two or more frames stack inone AC, the EDCA MAC may attempt to transmit a number of frames. If anSTA has already sent one frame and the STA may transmit a next frame inthe same AC within the remaining TXOP time and receive an ACK thereto,the STA attempts transmission of the frame after an SIFS time interval.A TXOP constraint value may be transferred from the AP to the STA. Incase the size of a data frame to be transmitted is in excess of the TXOPconstraint value, the STA may fragment the frame into a number ofsmaller frames, and the STA may transmit the smaller frames within arange not exceeding the TXOP constraint value.

FIG. 12 is a concept view illustrating a backoff procedure of an EDCA.

Referring to FIG. 12, each traffic data transmitted from an STA has apriority, and a backoff procedure may be conducted based on acontentious EDCA scheme. For example, the priorities respectivelyassigned to the traffics, as set forth above in Table 2, may beseparated into eight, for example. As described above, one STA hasdifferent output queues depending on priorities, and each output queueis operated according to the EDCA rules. Each output queue may transmittraffic data using different AIFSs (Arbitration Interframe Spaces)according to each priority instead of the conventionally used DIFSs (DCFInterframe Spaces). Further, in case STAs are supposed to transmittraffics having different priorities at the same time, a traffic havinga higher priority is transmitted earlier than the others, preventingcollision in the terminal.

A backoff occurs under the following situations. A backoff is used whenthe frames transmitted from terminals cause collision and thusre-transmission is needed. To initiate a backoff, a terminal sets anybackoff time in its backoff timer using Equation 2 below:

T _(b) [i]=Random(i)×SlotTime  <Equation 2>

Here, Random(i) is a function that generates any integer between 0 andCW[i] using a uniform distribution. CW[i] is a contention window betweenthe minimum contention window CWmin[i] and the maximum contention windowCWmax[i], and i is a traffic priority. At every collision, a newcontention window CWnew[i] is computed using the following Equation 3including a previous window CWold[i]:

CW _(new) [i]=((CW _(old) [i]+1)×PF)−1  <Equation 3>

Here, PF is computed according to the procedure defined in the IEEE802.11e standard. CWmin[i], AIFS[i], and PF value may be transmittedfrom the AP using a QoS parameter set element that is a managementframe.

(2) HCCA

The HCCA protocol uses an HC (Hyper Coordinator) that is positioned inan AP for centralized management on radio medium access. Since the HCperforms integrated and centralized management on the radio medium,contention over radio medium access between STAs may be reduced, andexchange between data frames may be left in a short transmission delaytime (SIFS), thus increasing network efficiency.

The HC controls transmission delay and scheduling by defining, in aparameter, a QoS characteristic for a particular traffic required by anapplication service to support QoS. Prior to the transmission of theparameterized QoS traffic, the HC establishes a virtual connection thatis referred to as a traffic stream. The traffic stream may correspond toeach of uplink from STA to AP, downlink from AP to STA, or direct linkfrom STA to STA. In order to configure a traffic stream between an APand an STA, QoS demand parameters such as delay time and trafficcharacteristics such as frame size and average transmission speed areexchanged through a mutual negotiation process.

In case the HC transmits a QoS CF-Poll frame to an STA, a TXOP limitvalue that is a service provision time allowed to the STA is included inthe QoS control field. In other words, the HC controls allocation of amedium access time using the TXOP. The TXOP limit value is determined bya TSPEC. The TSPEC is requested by a station, and an AP determineswhether to accept or decline the request for the TSPEC depending onnetwork circumstances.

Once a traffic stream is configured, the HC provides contracted QoS byallocating a radio band required for the configured traffic streambetween the AP and the STA. At a non-contention period of the HCCA, theHC has a right to control the medium, and if required, even at acontention period, the HC obtains a right to control the medium bytransmitting a QoS CF-Poll frame after as long a delay time as the PIFS.

FIG. 13 is a conceptual diagram illustrating a polled TXOP timing.

Referring to FIG. 13, a polled STA that possesses a TXOP receives a QoSCF poll frame to transmit multiple frames with an authority of thechannel access for a time as much as a TXOP limit value designated inthe QoS CF poll frame. In this case, other STAs configure its ownnetwork allocation vector (NAV) by collecting a TXOP time and apredetermined time after receiving the QoS CF poll frame even though notcorresponding thereto and do not contend with each other for the channelaccess during the corresponding time.

Consequently, an HC needs to schedule appropriate transmission of theQoS CF poll frame in order to meet contracted QoS requirements. In thecase of the radio medium, since a condition of the channel depending onthe time or position is diversified, making an efficient schedulingalgorithm becomes a primary element in supporting the QoS. An excellentscheduling algorithm permits more traffic streams while not breaching aQoS contract to improve the performance of the wireless network.

After the STA receives the beacon frame or the probe response frame,multiple STAs may attempt to simultaneously access the AP. In this case,there may be a higher probability that the multiple STAs will collidewith each other by simultaneously performing the channel access. In aninitial access procedure of the STA in the related art, the STAtransmits an association request frame by using access parameters (e.g.,CWmin, CWmax, and AIFSN) corresponding to AC_VO at the time oftransmitting the association request frame. In this case, there a higherprobability that the multiple STAs will simultaneously access the AP andin this case, the initial access procedure of the STA may be delayed.

In the embodiment of the present invention, a method for distributing atransmission timing of the association request frame at the time oftransmitting association request frames of multiple terminals to the APwill be disclosed. Hereinafter, the method is disclosed based on theassociation request frame in the embodiment for easy description, butthe method may be applied even to another management frame (e.g., anauthentication request frame) and the embodiment is also included in theclaims of the present invention.

FIG. 14 is a conceptual diagram illustrating an initial link configuringmethod according to an embodiment of the present invention.

According to the embodiment of the present invention, the STA mayreceive the beacon frame or the FILS discovery frame at the time ofperforming passive scanning. The beacon frame or the FILS discoveryframe may be received by multiple STA that exists around the AP. In thiscase, the timing when the multiple STAs that receive the beacon frame orthe FILS discovery frame performs the initial link setup (alternatively,the initial channel access) in order to associate with the AP may beoverlapped. Accordingly, when the multiple STAs perform the initial linksetup, the STA may collide with each other.

In the embodiment of the present invention, in order to solve theproblem, a method that permits only transmission of a terminal thatattempts the initial access during a predetermined time interval bydefining a predetermined time to reduce a possibility that the STAs willcollide with each other at the time of performing the initial link setupwill be disclosed. Hereinafter, the predetermined time interval will bedefined and used as a term called a protected channel access interval inthe embodiment of the present invention. The protected channel accessinterval may be used as a term called an initial protected link setupinterval as another term.

In the protected channel access interval, frames (e.g., a data frame andanother management frame) of already associated terminals aretransmitted after the protected channel access interval to limit channelaccess of another STA that does not perform the initial link setup inthe protected channel access interval. Information on the protectedchannel access interval may be transmitted to the STA through the beaconframe or the FILS discovery frame.

Referring to FIG. 14, the AP and two STAs (a first STA and a second STA)that set up the initial link setup around the AP and one STA (a thirdSTA) which already associates with the AP through the initial link setupmay exist already in the BSS. Two STAs that perform the initial linksetup and one STA that already performs the initial link setup mayreceive the beacon frame or the FILS discovery frame transmitted by theAP. The information on the protected channel access interval may beincluded in the beacon frame and the FILS discovery frame. The first STAand the second STA may acquire the information on the protected channelaccess interval based on the beacon frame or the FILS discovery frameand transmit the management frames (e.g., the authentication requestframe, the association request frame, and the like) for the initial linksetup in the corresponding interval. The third STA may also acquire theinformation on the protected channel access interval based on the beaconframe or the FILS discovery frame. The third STA does not transmit theframe to the AP in the protected channel access interval, but maytransmit the frame to the AP by performing the channel access in aninterval other than the protected channel access interval. By using themethod, the already associated STA does not occupy the channel whenother STAs perform the initial link setup to reduce the collision whichoccurs at the time of performing the initial link setup. Accordingly,the initial channel access of the STA that performs the initial channelaccess may be rapidly performed.

Additionally, the initial channel access timing of the STA that performsthe initial channel access in the protected channel access interval maybe distributed. The embodiment will be additionally described below inthe embodiment of the present invention.

FIG. 15 is a conceptual diagram illustrating a frame includinginformation on a channel access protection section according to anembodiment of the present invention.

In FIG. 15, the frame including the information on the protected channelaccess interval may be the beacon frame or the FILS discovery frame.

The protected channel access interval may include information on aninterval in which the terminal performing the initial link setuptransmits the frames (e.g., the authentication request frame, theassociation request frame, and the like) for the initial link setup. Forexample, when the information on the protected channel access intervalis set to 1, the set 1 may instruct the AP to permit only thetransmission of the frame for performing the initial channel access inthe protected channel access interval. On the contrary, when theinformation on the protected channel access interval is set to 0, theset 0 may instruct the AP to permit even transmission of another framein addition to the frame for performing the initial channel access inthe protected channel access interval.

A value for an interval may be included in the protected channel accessinterval specific to the information 1500 on the protected channelaccess interval. The STA may acquire information on an interval used forthe initial link setup based on the information 1500 on the protectedchannel access interval. For example, information 1520 on a protectedchannel access interval start point and information 1540 on a protectedchannel access interval end point may be included in the information1500 on the protected channel access interval. For example, theinformation 1520 on the protected channel access interval start pointmay include information on a time point when the protected channelaccess interval starts based on a reference time point (e.g., the timepoint when the beacon frame, the FILS discovery frame, or the FILSdiscovery frame is received). Further, the information 1540 on theprotected channel access interval end point may include information onthe time when the protected channel access interval ends. The unit ofthe information 1500 on the protected channel access interval may bemicro second (ms).

The STA may acquire information on the timing of performing the channelaccess based on the received information on the protected channel accessinterval.

Hereinafter, a method for distributing the initial channel access timingof the STA that performs the initial channel access in the protectedchannel access interval will be disclosed in the embodiment.

FIG. 16 is a conceptual diagram illustrating an initial access method ofan STA according to an embodiment of the present invention.

Referring to FIG. 16, the AP 1600 may determine channel statusinformation (e.g., a congestion status of a radio link). The AP 1600 mayuse various methods in order to determine the channel statusinformation. For example, the AP 1600 may determine the channel statusbased on the frame received from the neighboring STA or request theinformation on the channel status to the STA, and acquire informationregarding whether the radio link (alternatively, channel) is congestedfrom the STA as a response thereto. Further, the AP may acquire theinformation on the channel status from another AP.

According to a result of determining the channel status of the AP 1600,when the congestion status of the radio link (alternatively, channel) ismore than a threshold value, the AP 1600 may allocate the accessparameters (e.g., IFS, CWmin, CWmax, and TXOP) to STAs 1610, 1620, 1630,and 1640 for each scanning access class through the beacon frame 1605.Hereinafter, in the embodiment of the present invention, the presentinvention will be described on the assumption that access parameter setscorresponding to the respective scanning access classes are transmittedthrough the beacon frame for easy description. According to theembodiment of the present invention, the access parameter set may betransmitted for each scanning access class through not the beacon framebut the FILS discovery frame. Further, the access parameter set for eachscanning class may be transmitted in various information formats. Forexample, only information on an access parameter in which the scanningaccess class is not indexed may be transmitted. The access parameter setis an expression assuming that the plurality of access parameters (e.g.,IFS, CWmin, CWmax, and TXOP) are included. According to the embodimentof the present invention, one access parameter may be set for eachaccess class and this case may also be included in the claims of thepresent invention.

The AP 1600 may also transmit the information on the congestion statusof the radio link to the STAs 1610, 1620, 1630, and 1640 through thebeacon frame 1605. The information on the congestion status of the radiolink may be used as information on a channel congestion status asanother term. For example, the AP 1600 may determine the information onthe congestion status of the radio link based on information on thenumber of STAs which are associated at present and determine that theradio link is congested when the number of STAs which are associated atpresent is more than a set threshold value.

The information on the congestion status of the radio link may beindicated by, for example, 0 and 1. When the information on thecongestion status of the radio link is 0, it may be indicated that radiolink congestion is equal to or less than a threshold value and when theinformation on the congestion status of the radio link is 1, it may beindicated that the radio link congestion is more than the thresholdvalue. The STAs 1610, 1620, 1630, and 1640 may transmit to the AP 1600the management frame (e.g., the association request frame) based oninformation on the access parameter depending on the scanning accessclass included in the beacon frame 1605 when the information on thecongestion status of the radio link included in the received beaconframe 1605 is 1.

When the information on the congestion status of the radio link includedin the received beacon frame 1605 is 0, the STA applies the AC_VO whichis the access class of the association request frame defined in a QoSmanagement frame (QMF) policy in the related art to transmit theassociation request frame to the AP by using the access parametercalculated based on the AC_VO.

The scanning access class may be configured by a plurality of classes.The STA 1610, 1620, 1630, and 1640 may use a specific access parameterin order to transmit the association response frame. Hereinafter, theembodiment of the present invention discloses, for example, a method inwhich four scanning access classes are defined and the STA 1610, 1620,1630, and 1640 transmit the management frame (e.g., the associationrequest frame) based on the access parameter depending on the respectivescanning access classes.

Four scanning access classes may be defined as a first scanning accessclass, a second scanning access class, a third scanning access class,and a fourth scanning access class. An access parameter set may beconfigured, in which at least one access parameter is different for eachof the respective scanning access classes. Hereinafter, the presentinvention will be described on the assumption that all of the accessparameters included in the access parameter set corresponding to thescanning access class are different for easy description in theembodiment of the present invention.

For example, the access parameter included in the access parameter setmay be configured so that as the scanning access class has a largervalue, the STA performs the initial link setup more rapidly. Forexample, when the scanning access class has the larger value, at leastone access parameter among IFS, CWmin, and CWmax may be set to a valuesmaller than that when the scanning access class is a smaller value.Based on the method for configuring the access parameter set, when thescanning access class has the larger value, the STA discovers a smallIFS interval and sets a small back-off time to access the channel,thereby increasing the priority of the initial link setup. Further, asthe scanning access class has the larger value, a larger value may beallocated to the TXOP value. By allocating the larger value to the TXOPvalue, preferentially, as the scanning access class has the largervalue, the priority of the initial link setup may be increased. That is,a time required for the association of the STA or the priority may varydepending on the scanning access class, that is, the access parameterset selected by the STA. Since the initial link setup timing isdistributed depending on the scanning access class at the time ofperforming the initial link setup by using such a method, a phenomenonmay be prevented, in which a collision occurs at the time of performingthe initial link setup of the STA to the AP.

That is, according to the embodiment, the protected channel accessinterval previously described in FIGS. 14 and 15 is configured and theinitial link setup timing of the STA is distributed in the protectedchannel access interval to perform the initial link setup.

As illustrated in FIG. 16, each of the STAS 1610, 1620, 1630, and 1640that receive the same beacon frame 1605 from the AP 1600 may configurethe scanning access class (alternatively, the access parameter set).When the radio status congestion information of the beacon frameindicates that the radio link is congested, the STA may perform theinitial link setup depending on the access parameter set selected in theprotected channel access interval.

For example, the first STA 1610 may decide the first scanning accessclass, the second STA 1620 may decide the second scanning access class,the third STA 1630 may decide the third scanning access class, and thefourth STA 1640 may decide the fourth scanning access class. In thiscase, the STA may perform the channel access based on the accessparameter depending on each decided scanning access class. For example,the first STA 1610 may perform the channel access based on a firstaccess parameter depending on the first scanning access class, thesecond STA 1620 may perform the channel access based on a second accessparameter depending on the second scanning access class, the third STA1630 may perform the channel access based on a third access parameterdepending on the third scanning access class, and the fourth STA 1640may perform the channel access based on a fourth access parameterdepending on the fourth scanning access class.

The first STA and the fourth STA may perform the initial link setupbased on the timing distributed in the protected channel accessinterval. By using such a method, the plurality of STAs 1610, 1620,1630, and 1640 that receives the beacon frame 1605 simultaneously maydistribute the transmission timing of the transmitted management frame(e.g., the association request frame) at the time of performing thechannel access.

FIG. 17 is a conceptual diagram illustrating channel access of an STAdepending on a scanning access class according to an embodiment of thepresent invention.

Referring to FIG. 17, an STA 1710 corresponding to the first scanningaccess class to an STA 1740 corresponding to the fourth scanning accessclass may perform the initial link setup based on the distributed timingin the protected channel access interval.

The STA 1740 corresponding to the fourth scanning access class may firstaccess the channel based on a fourth access parameter 1745 and next, anSTA 1730 corresponding to the third scanning access class may access thechannel based on a third access parameter 1735. Next, an STA 1720corresponding to the second scanning access class may access the channelbased on a second access parameter 1725 and an STA corresponding to afirst scanning access class 1710 may access the channel based on a firstaccess parameter 1715. That is, a lot of STAs may be controlled not tosimultaneously access the AP by distributing the channel access timingdepending on the scanning access class.

Hereinafter, the embodiment of the present invention discloses a methodin which the STA decides the scanning access class.

When the radio link congestion status information of the beacon framereceived by the STA is 1, the STA selects one scanning access class totransmit the association request frame to the AP. For example, thefollowing method may be used in order for the STA to select one scanningaccess class.

The STA may select a random variable between 0 and 1. The STA may selectthe scanning access class according to the selected random variable.Table 3 given below shows the scanning access class depending on a rangeof the random variable selected by the STA.

TABLE 3 random variable Passive scanning access class 0 ≦ randomvariable < 0.25 First passive scanning access class 0.25 ≦ randomvariable < 0.5 Second passive scanning access class 0.5 ≦ randomvariable < 0.75 Thrid passive scanning access class 0.75 ≦ randomvariable < 1 Fourth scanning access class

The STA may randomly select the number between 0 and 1 and decide thescanning access class according to the selected random variable. The STAmay transmit the association request frame to the AP based on thedecided scanning access class. The scanning access class is distributedinto the first to fourth scanning access classes to be selectedaccording to the random variables randomly selected by the plurality ofSTAs. The association request frame is transmitted to the AP accordingto the distributed scanning access classes to allow the terminal todistribute the channel access timing in the protected channel accessinterval to transmit the association request frame.

Table 4 given below shows the access parameter set according to thescanning access class.

TABLE 4 Passive IFS(For scanning example, access class CWmin CWmax AIFS)First passive (Default CWmin (Default CWmax (Default AIFS scanningaccess of AC_VO)*8 of AC_VO)*8 of AC_VO)*8 class Second passive (DefaultCWmin (Default CWmax (Default AIFS scanning access of AC_VO)*4 ofAC_VO)*4 of AC_VO)*4 class Third passive (Default CWmin (Default CWmax(Default AIFS scanning access of AC_VO)*2 of AC_VO)*2 of AC_VO)*2 classFourth passive (Default CWmin (Default CWmax (Default AIFS scanningaccess of AC_VO) of AC_VO) of AC_VO) class

Referring to Table 4, the access parameter sets (e.g., CWmin, CWmax, andIFS) according to the scanning access classes may be defined. The accessparameter sets according to the respective scanning access classes maybe decided with the access parameter value corresponding to the AC_VOCin the EDCA in the related art as a reference value. The CWmin, CWmax,and IFS values included in the access parameter sets may be set todecreased values from the first scanning access class to the fourthscanning access class. The STA corresponding to the scanning accessclass having the larger value may perform the initial link setup morerapidly than the STA corresponding to the scanning access class havingthe smaller value in the protected channel access interval byconfiguring the access parameter set according to the scanning accessclass.

The access parameter set disclosed in Table 4 is an exemplary accessparameter. Different access parameter sets may be defined in order toperform the initial link setup of different STAs according to thescanning access class and the embodiment is also included in the claimsof the present invention.

Table 5 given below shows another example representing the accessparameter according to the scanning access class.

TABLE 5 Passive IFS(For scanning example, access class CWmin CWmax AIFS)First passive CWmin of AC_BK CWmax of AC_BK AIFS of scanning AC_BKaccess class Second passive CWmin of AC_BE CWmax of AC_BE AIFS ofscanning AC_BE access class Third passive CWmin of AC_VI CWmax of AC_VIAIFS of scanning AC_VI access class Fourth passive CWmin of AC_VO CWmaxof AC_VO AIFS of scanning AC_VO access class

The access parameter set according to the scanning access class may beconfigured as above based on the EDCA parameter in the related art.Access parameter information according to AC_BK, AC_BE, AC_VI, and AC_VOis disclosed in a 8.4.2.31 EDCA parameter set element of IEEE DraftP802.11-REVmb™/D12, November 2011 (IEEE Standard for InformationTechnology—Telecommunications and information exchange betweensystems—Local and metropolitan area networks—Specific requirements Part11, Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)Specifications) disclosed in November 2011.

Table 6 given below exemplarily shows the access parameters according toAC_BK, AC_BE, AC_VI, and AC_VO when dot11OCBActivated defined in theIEEE Draft P802.11-REVmb™/D12 in the related art has a true value. Theaccess parameters included in the access parameter sets such as CWmin,CWmax, AIFSN, and TXOP may be configured differently according to AC_BK,AC_BE, AC_VI, and AC_VO.

TABLE 6 TXOP Limit OFDM/CCK- AC CWmin CWmax AIFSN OFDM PHY AC_BK aCWminaCWmax 9 0 AC_BE aCWmin aCWmax 6 0 AC_VI (aCWmin + aCWmin 3 0 1)/2-1AC_VO (aCWmin + (aCWmin + 2 0 1)/4-1 1)/2-1

Referring back to Table 5, in the embodiment of the present invention,the access parameter according to the scanning access class may bedecided based on the access parameter sets of AC_BK, AC_BE, AC_VI, andAC_VO used in the EDCA in the related art.

Hereinafter, a method for applying a scaling element of the accessparameter will be disclosed.

The AP may change the access parameter according to the radio linkcongestion status information included in the beacon frame, the FILSdiscovery frame, or the probe response frame. For example, the APtransmits an additional scaling element (e.g., N) to the STA to allowthe STA to change the access parameter used at the time of performingthe initial link setup. The STA may change the access parameter setconfigured based on the received scaling element and perform the initiallink setup based on the changed access parameter set.

For example, as shown in Table 4 described above, the STA may decide theaccess parameter to be used in the initial link setup based on defaultaccess parameters (default, CWmin, default CWmax, and default IFS) andthe scaling element transmitted by the AP. When the scaling element hasa value of N, the access parameters which the STA will use in theinitial link setup may be decided as (CWmin*N), (CWmax*N), and (AIFS*N).The STA may transmit the association request frame based on the accessparameter decided in the protected channel access interval.

For example, as shown in Table 7 given below, the access parameterdefined in each scanning access class of Table 4 is set as the defaultaccess parameter and each access parameter is multiplied by N to performscaling.

TABLE 7 Passive IFS(For scanning example, access class CWmin CWmax AIFS)First passive (Default CWmin (Default CWmax (Default AIFS scanningaccess of AC_VO)*8*N of AC_VO)*8*N of AC_VO)*8 class Second passive(Default CWmin (Default CWmax (Default AIFS scanning access ofAC_VO)*4*N of AC_VO)*4*N of AC_VO)*4 class Third passive (Default CWmin(Default CWmax (Default AIFS scanning access of AC_VO)*2*N of AC_VO)*2*Nof AC_VO)*2 class Fourth passive (Default CWmin (Default CWmax (DefaultAIFS scanning access of AC_VO)*N of AC_VO)*N of AC_VO)*N class

By using such a method, the access parameter of the STA may be set moreadaptively according to the channel situation. The aforementionedembodiment discloses that the STA decides the access parameter throughthe scanning access class decided based on the random variable for easydescription. However, the STA may decide the random variable andimmediately decide the access parameter according to the randomvariable. That is, the STA may decide the access parameter set which theSTA will use based on the random variable without a procedure fordeciding a separate index called the scanning access class.

For example, when the information on the channel status of the receivedbeacon frame or FILS discovery frame indicates that the radio link iscongested, the STA may select the random variable. The STA may selectone access parameter set among the plurality of access parameters basedon the selected random variable. The STA may transmit the associationrequest frame to the AP by performing the initial channel access basedon the selected access parameter. That is, the scanning access classdisclosed in the embodiment of the present invention serves as one indexfor the STA to select the access parameter set and the STA may selectone of the access parameter sets transmitted through the beacon framewithout indexing the scanning access class.

According to yet another embodiment of the present invention, theterminal may configure the access parameter set by a value acquired bymultiplying the default access parameter by N without particularlydefining the scanning access class. That is, the terminal may performthe initial link setup based on the value of N which is the scalingelement included in the frame transmitted by the AP without deciding thescanning access class. By such a method, the N value may vary dependingon the STA that receives the beacon frame, the STA that receives theprobe response frame, and the STA that receives the FILS discovery frameand the STAs may perform the channel access based on different accessparameters. The STA decides the default CWmin*N, default CWmax*N, anddefault AIFS*N as the access parameters based on the N value which isthe scaling element received through the frame to perform the channelaccess in the protected channel access interval.

According to the embodiment of the present invention, the terminal mayadaptively select the scanning access class according to a radio linkcongestion level. In the aforementioned channel access method of theSTA, only when the radio link is congested based on radio linkcongestion level information transmitted by the AP (for example, whenthe radio link congestion level is 0), an initial link setup procedureaccording to the scanning access class is performed. Moreover, even whenthe radio link congestion level information transmitted by the APindicates that the radio link is not congested (for example, when theradio link congestion level is 1), the initial link setup according tothe scanning access class may be performed.

In the embodiment of the present invention, the scanning access classaccording to a random variable interval selected by the STA isconfigured differently according to the radio link congestion level toselect the scanning access class or the access parameter set atdifferent ratios according to the radio link congestion level. As thesame meaning, the access parameter set according to the random variableselected by the STA may be configured differently according to the radiolink congestion level. Hereinafter, the present invention will bedescribed on the assumption that the STA decides the scanning accessclass for easy description in the embodiment of the present invention.However, as described above, the STA may directly decide the accessparameter set without the procedure of deciding the scanning accessclass.

For example, when the radio link congestion level of the beacon framereceived by the STA indicates that the radio link is not congested,relative more STAs may be configured to select a higher scanning accessclass (e.g., the third scanning access class or the fourth scanningaccess class). For example, a range of the random variable in which thethird scanning access class or the fourth scanning access class may beselected may be extended so as for the relatively more STAs to selectthe higher scanning access class as described above. Table given belowis a table for dividing the scanning access class according to therandom variable.

TABLE 8 random variable Passive scanning access class 0 ≦ randomvariable < 0.15 First passive scanning access class 0.15 ≦ randomvariable < 0.3 Second passive scanning access class 0.3 ≦ randomvariable < 0.5 Thrid passive scanning access class 0.5 ≦ random variable< 1 Fourth scanning access class

Fourth Passive Scanning Access Class

Referring to Table 8, the interval of the random variable selected asthe third scanning access class and the fourth scanning access class maybe extended so as to select the third scanning access class and thefourth scanning access class more frequently according to the randomvariable selected by the STA. The interval of the random variableaccording to the scanning access class of Table 8 is an intervalarbitrarily defined so as for the STA to decide the higher scanningaccess class with a relatively higher probability according to therandom variable selected by the STA. The random variable intervalconfigured in Table 8 may vary.

Further, when it is indicated that the radio link congestion level islow in the received beacon frame, relatively more STAs may be configuredto select a lower scanning access class (e.g., the first scanning accessclass or the second scanning access class). For example, a range inwhich the first scanning access class or the second scanning accessclass may be extended by the random variable selected by the STA so asfor the relatively more STAs to select the lower scanning access classas described above. Table 9 given below is a table for dividing thescanning access class according to the random variable.

TABLE 9 random variable Passive scanning access class 0 ≦ randomvariable < 0.5 First passive scanning access class 0.5 ≦ random variable< 0.7 Second passive scanning access class 0.7 ≦ random variable < 0.85Thrid passive scanning access class 0.85 ≦ random variable < 1 Fourthscanning access class

Referring to Table 9, the interval of the random variable selected asthe first scanning access class and the second scanning access class maybe extended so as to select the first scanning access class and thesecond scanning access class more frequently according to the randomvariable selected by the STA. The interval of the random variableaccording to the scanning access class of Table 9 is an intervalarbitrarily defined so as for the STA to decide the lower scanningaccess class with the relatively higher probability according to therandom variable selected by the STA. The random variable intervalconfigured in Table 9 may vary.

The aforementioned embodiment discloses a method in which the STAreceives at least one pieces of information of the information on theprotected channel access interval, the information on the linkcongestion status, and the information on the access parameter accordingto the scanning access class based on the beacon frame and/or the FILSdiscovery frame and performs the channel access based on the receivedinformation. However, even the probe response frame received when theSTA performs active scanning may include at least one piece ofinformation including the information on the protected channel accessinterval, the information on the link congestion status, and theinformation on the access parameter according to the scanning accessclass, and a subsequent operation of the STA may be performed similarlyto that when at least one piece of information of the information on theprotected channel access interval, the information on the linkcongestion status, and the information on the access parameter accordingto the scanning access class based on the beacon frame and/or the FILSdiscovery frame is received.

FIG. 18 is a conceptual diagram illustrating a frame format according toan embodiment of the present invention.

In FIG. 18, the AP encapsulates information 1800 on the protectedchannel access interval, information 1820 on the link congestion status,and information 1840 on the access parameter set included in the beaconframe, the FILS discovery, and the probe response frame to transmit thebeacon frame, the FILS discovery, and the probe response frame.

The information 1800 on the protected channel access interval mayinclude information on an interval in which the terminal performing theinitial link setup transmits the frames (e.g., the authenticationrequest frame, the association request frame, and the like) for theinitial link setup. For example, when the information on the protectedchannel access interval is set to 1, the set 1 may instruct the AP topermit only the transmission of the frame for performing the initialchannel access in the protected channel access interval. On thecontrary, when the information on the protected channel access intervalis set to 0, the set 0 may instruct the AP to permit even transmissionof another frame in addition to the frame for performing the initialchannel access in the protected channel access interval. A value for aninterval may be included in a protected channel access interval specificto the information on the protected channel access interval. The STA mayacquire information on an interval used for the initial link setup basedon the information 1800 on the protected channel access interval. Forexample, the protected channel access interval start point may includeinformation on a time point when the protected channel access intervalstarts based on a reference time point (e.g., the time point when thebeacon frame, the FILS discovery frame, or the FILS discovery frame isreceived or received). Further, the protected channel access intervalend point may include information on the time when the protected channelaccess interval ends. The unit of the information on the protectedchannel access interval may be micro second (ms).

The radio link congestion status information 1820 may includeinformation on a channel status of a current AP. For example, accordingto a result in which the AP determines the channel status, when thechannel is congested, the radio link congestion status information 1802is set to 0 to be transmitted to the STA. On the contrary, according tothe result in which the AP determines the channel status, when thechannel is not congested, the radio link congestion status information1802 is set to 1 to be transmitted. Whether the channel is congested maybe determined based on, for example, a frame received from a neighboringSTA or the information on the channel status may be requested to the STAand the radio link congestion status information 1820 may be acquiredbased on the requested information. Further, the AP may acquire theinformation on the channel status from another AP. For example, the APmay count and measure the management frames (e.g., the probe requestframe, the association request frame, and the authentication requestframe) which the AP receives for the purpose of the initial link setup.As yet another example, the AP may define a link level based on loadinformation of the BSS.

The access parameter set which the STA will use in the initial linksetup may be decided differently based on the information 1820 on theradio link congestion status.

The information 1840 on the access parameter set may include theplurality of access parameter sets for the STA to perform the initiallink setup at the distributed timing.

The STA may decide the scanning access class and perform the initialchannel access based on the access parameter decided according to theaccess parameter information 1820 depending on the received scanningaccess class. Alternatively, the STA may decide the access parameter setaccording to the random variable and perform the initial link setupbased on the decided access parameter set.

The access parameter set according to the scanning access class is notseparately transmitted through the beacon frame, the FILS discoveryframe, or the probe response frame and may be defined in the AP and/orthe STA in advance. In this case, the beacon frame, the FILS discoveryframe, or the probe response frame may not include the access parameterinformation depending on the scanning access class.

Further, the beacon frame, the FILS discovery frame, or the proberesponse frame may additionally include an access parameter scalingelement depending on the scanning access class.

FIG. 19 is a conceptual diagram illustrating a frame format according tothe embodiment of the present invention.

Referring to FIG. 19, the beacon frame, the FILS discovery frame, or theprobe response frame additionally include a scaling element (or factor)1900 to be transmitted.

The STA may define the default access parameters (default CWmin, defaultCWmax, and default IFS) and decide an access parameter value which theSTA will use based on the scaling element 1900 transmitted by the AP. Asdescribed above, the default access parameter is multiplied by N whichis the scaling element to decide the access parameter.

According to yet another embodiment of the present invention, theprotected channel access interval may be configured based on thepriority.

The protected channel access interval may be expressed as the protectedchannel access interval as another term and a priority field may beexpressed as information on an STA that is accessible to the channel inthe protected channel access interval.

For example, the beacon frame, the FILS discovery frame, or the proberesponse frame includes the priority field to be transmitted. Thepriority field may include information on the STA that may perform thechannel access in the protected channel access interval. For example,the priority field may be defined as shown in Table 10 given below.

A user priority may be, for example, information corresponding to theaforementioned scanning access class. The user priority may decidedaccording to the random variable decided by the STA and the randomvariable interval may be for deciding the user priority may beconfigured differently according to the channel status information.

TABLE 10 Initial link bit setup priority Description Bit 0 0 Userpriority 4~7 STA performing initial link setup Bit 1 1 User priority 0~3STA performing initial link setup Bit 2 2 STA performing initial linksetup Bit 3 3 STA already performing initial link setup

Referring to Table 10, when bit 0 has a value of ‘1’, STAs correspondingto user priorities 4 to 7 in the protected channel access interval mayperform the initial link setup. When bit 1 has the value of 1 STAscorresponding to user priorities 1 to 3 in the protected channel accessinterval may perform the initial link setup. When bit 2 has the value of‘1’, an STA that performs the initial link setup in the protectedchannel access interval may perform the initial link setup. When bit 3has the value of ‘1’, an STA that already performs the initial linksetup in the protected channel access interval may perform the channelaccess. The user priority may be decided by various methods. Forexample, the user priority may be selected based on the random variableselected by the STA similarly to the method for deciding the scanningaccess class. Further, the user priority may be decided according to aspecification of the STA.

When a bit of the priority bit is set to 0, an STA corresponding to thecorresponding bit may not perform the initial link setup during theprotected channel access interval or may not transmit traffic data tothe AP through the channel access.

On the contrary, when the priority bit is set to 1, the STAcorresponding to the corresponding bit may perform the initial linksetup during the protected channel access interval or may transmit thetraffic data to the AP through the channel access.

In Table 10, a configuration of the priority field is one example. Thepriority field as a field including information on the priority toperform the channel access in the protected channel access interval maybe decided in various formats. For example, when a first bit included ina bitmap is 1, an STA corresponding to a first channel access prioritymay perform the initial channel access in the protected channel accessinterval and when a second bit included in the bitmap is 1, an STAcorresponding to a second channel access priority may perform theinitial channel access in the protected channel access interval.Further, when a third bit included in the bitmap is 1, the bit of 1 mayinstruct an STA that already performs the initial channel access toperform the channel access in the protected channel access interval.

When the STA receives a frame including information on the channelstatus, information on the protected channel access interval, andinformation (e.g., the priority field) on the STA that may perform thechannel access in the protected channel access interval from the AP, theSTA may perform the following operation. When the information on thechannel status indicates the congestion of the radio link, the STA maydecide the channel access priority. For example, the STA may decide thechannel access priority based on the random variable as described above.The STA may perform the initial channel access in the protected channelaccess interval based on the decided channel access priority and theinformation on the STA that may perform the channel access in theprotected channel access interval.

The STA may use the following method in order to decide the channelaccess priority. The STA may select one channel access priority among N(is a natural number of N>1) channel access priorities decided based onthe selected random variable. The random variable selected by the STAmay be included in one random variable range among N (is the naturalnumber of N>1) random variable ranges. N random variable ranges maycorrespond to N channel access priorities, respectively and one channelaccess priority selected by the STA may correspond to one randomvariable range. That is, the STA may select the channel access prioritycorresponding to the selected random variable.

When the channel status of the AP is not good, the information on theradio link congestion status may be set to 1 and the priority field maybe transmitted, but as yet another embodiment, when the AP does notinclude the information on the radio link congestion status and a linkstatus is not good, the channel access of the STA may be limited in theprotected channel access interval by transmitting only a link setupbitmap. That is, the STA may acquire information regarding whether thechannel access being limited in the protected channel access intervalaccording to existence of the priority field.

FIG. 20 is a conceptual diagram illustrating a channel access method ofan STA according to an embodiment of the present invention.

FIG. 20 illustrates an embodiment of a method in which the STA performsthe channel access based on the received priority field and theprotected channel access interval.

Referring to FIG. 20, for example, it is assumed that bit 3 of thepriority included in the beacon frame received by the STA may be set to0 and the information on the protected channel access interval isincluded. That is, the AP may transmit the beacon frame in which the bit3 of the priority field is set to 0 and which includes the informationon the protected channel access interval.

When the first STA and the second STA are STAs that perform the initiallink setup and the third STA is an STA that performs the initial linksetup, the following operation may be performed.

Only the first STA and the second STA that perform the initial linksetup in the protected channel access interval may perform the initiallink setup. The first STA and the second STA may transmit theassociation request frame in the protected channel access interval. Thethird STA already associated with the AP, which performs the initiallink setup may not perform the channel access in the protected channelaccess interval. The third STA already associated with the AP maytransmit the frame through the channel access in an interval over theprotected channel access interval.

The priority may be given to the channel access of the STA for theinitial link setup based on the configuration of the priority field andthe protected channel access interval.

FIG. 21 is a conceptual diagram illustrating a channel access method ofan STA according to an embodiment of the present invention.

FIG. 21 illustrates an embodiment of a method in which the STA performsthe channel access based on the received priority field and theprotected channel access interval.

Referring to FIG. 21, for example, it may be assumed that bit 0 of thepriority included in the beacon frame received by the STA may be set to1, remaining bits 1 to 3 may be set to 0, and the information on theprotected channel access interval is included. That is, the AP may set abit in which the priority field corresponds to ‘1000’ in the beaconframe and transmit the bit including the information on the protectedchannel access interval.

In this case, only the second STA corresponding to user priorities 4 to7 in the protected channel access interval may perform the initial linksetup. The second STA may transmit the association request frame in theprotected channel access interval. The first STA corresponding to userpriorities 1 to 3 and the third STA already associated with the AP,which performs the initial link setup may not perform the channel accessin the protected channel access interval. The first STA corresponding touser priorities 1 to 3 and the third STA already associated with the AP,which performs the initial link setup may transmit the associationrequest frame and the frame through the channel access after theprotected channel access interval ends.

According to yet another embodiment of the present invention, the linksetup bitmap is defined in the priority field as shown in a table givenbelow and included in the beacon frame, the FILS discovery frame, or theprobe response frame to be transmitted.

TABLE 11 bit Description Bit 0 User priority 4~7 STA performing initiallink setup Bit 1 User priority 0~3 STA performing initial link setup Bit2 STA performing initial link setup Bit 3 STA already performing initiallink setup

Table 11 shows a link setup bitmap for representing whether to accessthe channel in the protected channel access interval. Table 11 is oneexample for the link setup bitmap.

When the bit included in the link setup bitmap of Table 11 is set to‘1’, the set 1 may instruct the STA corresponding to the bit set to 1not to transmit the frame in the protected channel access interval.

The AP may set the radio link congestion status information(alternatively, channel congestion status information) of the frame to 1and transmit the radio link congestion status information including thelink setup bitmap to the STA. For example, it may be assumed that the APsets the radio link congestion status information to 1, and sets bit 1in the link setup bitmap to 1 and transmits the set bit 1. Terminalscorresponding to user priorities 4 to 7 among terminals that perform theinitial link setup may determine that the channel status is not good fora time corresponding to the protected channel access interval. Theterminals corresponding to user priorities 4 to 7 among the terminalsthat perform the initial link setup may transmit the management framefor performing the initial link setup after the protected channel accessinterval elapses without performing the channel access in the protectedchannel access interval.

As yet another embodiment, when the AP does not include the informationon the radio link congestion status the AP and the link status is notgood, the AP transmits only the link setup bitmap to limit the channelaccess of the STA in the protected channel access interval. That is, theSTA may acquire the information regarding whether the channel accessbeing limited in the protected channel access interval according to theexistence of the priority field.

FIG. 22 is a conceptual diagram illustrating a frame format according tothe embodiment of the present invention.

Referring to FIG. 22, the beacon frame, the FILS discovery frame, or theprobe response frame may include a priority field 2200 and information2250 on the protected channel access interval.

As described above, the priority field 2200 may include information on apriority to perform the channel access in the protected channel accessinterval. As shown in Table 10, the priority field 2200 may include theinformation on the priority based specific bit information and includethe priority information in various information formats.

In the information 2250 on the protected channel access interval, avalue for an interval may be included in a specific protected channelaccess interval. The STA may acquire information on an interval used forthe initial link setup based on the information 2250 on the protectedchannel access interval. For example, information 2260 on a protectedchannel access interval start point and information 2270 on a protectedchannel access interval end point may be included in the information2200 on the protected channel access interval. For example, theinformation 2250 on the protected channel access interval start pointmay include information on a time point when the protected channelaccess interval starts based on a reference time point (e.g., the timepoint when the beacon frame, the FILS discovery frame, or the FILSdiscovery frame is transmitted or received). Further, the information2260 on the protected channel access interval end point may includeinformation on the time when the protected channel access interval ends.The unit of the information 2250 on the protected channel accessinterval may be micro second (ms).

The STA may acquire information on the timing of performing the channelaccess based on the received information on the protected channel accessinterval.

FIG. 23 is a block diagram illustrating a wireless device to which anembodiment of the present invention may apply.

Referring to FIG. 23, the wireless device 2300 may be an STA that mayimplement the above-described embodiments, and the wireless device 2300may be an AP or a non-AP STA (station).

The wireless device 2300 includes a processor 2320, a memory 2340, andan RF (Radio Frequency) unit 2360.

The RF unit 2360 may be connected with the processor 2320 totransmit/receive radio signals.

The processor 2320 implements functions, processes, and/or methods asproposed herein. For example, the processor 2320 may be implemented toperform the operation of the above-described wireless device accordingto an embodiment of the present invention.

For example, the processor 2320, in case the wireless device is an AP,may be implemented to generate a frame including information on achannel status, information on a protected channel access interval, andinformation on an STA which is accessible to a channel in the protectedchannel access interval and transmit the frame to STA.

Further, the processor 2320, in case the wireless device is an STA, maybe implemented to receive a frame including information on a channelstatus, information on a protected channel access interval, andinformation on an STA which is accessible to a channel in the protectedchannel access interval, from an access point (AP) and decide a channelaccess priority when the information on the channel status indicatesthat a radio link is congested. The processor 2320 may be implemented toperform the initial channel access in the protected channel accessinterval based on the decided channel access priority and theinformation on the STA which is accessible to the channel in theprotected channel access interval.

The processor 2320 may include an ASIC (Application-Specific IntegratedCircuit), other chipset, a logic circuit, a data processing device,and/or a converter that performs conversion between a baseband signaland a radio signal. The memory 2340 may include a ROM (Read-OnlyMemory), a RAM (Random Access Memory), a flash memory, a memory card, astorage medium, and/or other storage device. The RF unit 2360 mayinclude one or more antennas that transmit and/or receive radio signals.

When an embodiment is implemented in software, the above-describedschemes may be embodied in modules (processes, or functions, etc.)performing the above-described functions. The modules may be stored inthe memory 2340 and may be executed by the processor 2320. The memory2340 may be positioned in or outside the processor 2320 and may beconnected with the processor 2320 via various well-known means.

What is claimed is:
 1. A method in which a station (STA) performsinitial channel access in a wireless LAN, the method comprising:receiving, by the STA, a frame including information on a channelstatus, information on a protected channel access interval, andinformation on an STA which is accessible to a channel in the protectedchannel access interval, from an access point (AP); deciding, by theSTA, a channel access priority when the information on the channelstatus indicates that a radio link is congested; and performing, by theSTA, the initial channel access in the protected channel access intervalbased on the decided channel access priority and the information on theSTA which is accessible to the channel in the protected channel accessinterval, wherein the information on the protected channel accessinterval includes information on a time limited so as for only the STAwhich is accessible to the channel in the protected channel accessinterval to performs channel access.
 2. The method of claim 1, whereinthe channel access priority is one channel access priority among N (is anatural number of N>1) channel access priorities decided based on arandom variable selected by the STA, wherein the selected randomvariable is included in one random variable range among N (is thenatural number of N>1) random variable ranges, wherein the N randomvariable ranges correspond to the N channel access priorities,respectively, and wherein the one channel access priority corresponds tothe one random variable range.
 3. The method of claim 2, wherein thesize of the N random variable ranges is decided differently inaccordance with the information on the channel status.
 4. The method ofclaim 1, wherein the information on the STA which is accessible to thechannel in the protected channel access interval indicates an STA whichis permitted to access the channel in the protected channel accessinterval based on a bitmap.
 5. The method of claim 4, wherein when bit 1included in the bitmap is 1, the set bit 1 instructs an STAcorresponding to a first channel access priority to perform the initialchannel access in the protected channel access interval, wherein whenbit 2 included in the bitmap is 1, the set bit 2 instructs an STAcorresponding to a second channel access priority to perform the initialchannel access in the protected channel access interval, and whereinwhen bit 3 included in the bitmap is 1, the set bit 3 instructs an STAthat already performs the initial channel access to perform the channelaccess in the protected channel access interval.
 6. The method of claim1, wherein the frame is a beacon frame, a fast initial link setup (FILS)discovery frame, or a probe response frame.
 7. The method of claim 1,wherein the information on the protected channel access intervalincludes information on a start point of the protected channel accessinterval and information on an end point of the protected channel accessinterval.
 8. A station (STA) for performing scanning in a wireless LAN,the station comprising: an RF unit receiving a radio signal; and aprocessor operatively connected with the RF unit, wherein the processoris implemented to receive a frame including information on a channelstatus, information on a protected channel access interval, andinformation on an STA which is accessible to a channel in the protectedchannel access interval, from an access point (AP), decide a channelaccess priority when the information on the channel status indicatesthat a radio link is congested, and perform initial channel access inthe protected channel access interval based on the decided channelaccess priority and the information on the STA which is accessible tothe channel in the protected channel access interval, and theinformation on the protected channel access interval includesinformation on a time limited so as for only the STA which is accessibleto the channel in the protected channel access interval to performschannel access.
 9. The STA of claim 8, wherein the channel accesspriority is one channel access priority among N (is a natural number ofN>1) channel access priorities decided based on a random variableselected by the STA, wherein the selected random variable is included inone random variable range among N (is the natural number of N>1) randomvariable ranges, wherein the N random variable ranges correspond to theN channel access priorities, respectively, and wherein the one channelaccess priority corresponds to the one random variable range.
 10. TheSTA of claim 8, wherein the size of the N random variable ranges isdecided differently in accordance with the information on the channelstatus.
 11. The STA of claim 8, wherein the information on the STA whichis accessible to the channel in the protected channel access intervalindicates an STA which is permitted to access the channel in theprotected channel access interval based on a bitmap.
 12. The STA ofclaim 11, wherein when bit 1 included in the bitmap is 1, the set bit 1instructs an STA corresponding to a first channel access priority toperform the initial channel access in the protected channel accessinterval, wherein when bit 2 included in the bitmap is 1, the set bit 2instructs an STA corresponding to a second channel access priority toperform the initial channel access in the protected channel accessinterval, and wherein when bit 3 included in the bitmap is 1, the setbit 3 instructs an STA that already performs the initial channel accessto perform the channel access in the protected channel access interval.13. The STA of claim 8, wherein the frame is a beacon frame, a fastinitial link setup (FILS) discovery frame, or a probe response frame.14. The STA of claim 8, wherein the information on the protected channelaccess interval includes information on a start point of the protectedchannel access interval and information on an end point of the protectedchannel access interval.